ECG Challenge: A 48-year-old man without any known cardiac problems but with a history of rheumatoid arthritis for which he is receiving therapy with methotrexate presents to his rheumatologist for a routine examination. His pulse is noted to be irregular; therefore, he is sent to the emergency room for an ECG.
The rhythm is irregular, but there is a regular pattern of what appears to be group beating, with 3 QRS complexes followed by a pause. The first and third QRS complexes of the group have the same morphology. They are narrow (0.08 second) with a normal morphology. The axis is normal between 0° and +90° (positive QRS complex in leads I and aVF). Both of these QRS complexes are preceded by a P wave (+), which is positive in leads I, II, aVF, and V4 through V6. Hence, these are sinus complexes. The P wave is primarily negative in lead V1, consistent with a left atrial abnormality or left atrial hypertrophy. The middle or second QRS complex is wide (0.12 second) and has a morphology that is different from the sinus complexes. It has a morphology that resembles neither a typical right or left bundle branch block. It is not preceded by a P wave; thus, this is a premature ventricular complex. Note that there is no pause after the premature ventricular complex and that the PP intervals are constant (┌┐) and not altered by this premature complex; the sinus rate is 42 bpm (sinus bradycardia). These premature ventricular complexes are thus interpolated, and because every third QRS complex is a premature ventricular complex, this is ventricular trigeminy (ie, interpolated premature ventricular complexes in a trigeminal pattern). Although there is a P wave before each of the narrow QRS complexes, the PR interval is not the same. The sinus complex before the premature ventricular complex (the first of the 3 complexes) has a PR interval of 0.20 second (└┘), whereas the sinus complex after the premature complex (the third of the 3) has a PR interval of 0.28 second (└┘). This is the result of retrograde concealed conduction; that is, the premature ventricular impulse conducts retrogradely into the atrioventricular node but does conduct through it completely (it is concealed within the atrioventricular node), rendering it partially depolarized and partially refractory. The next sinus impulse can therefore get through the atrioventricular node, but it does slow at a slower rate because the atrioventricular node is still partially refractory. The QT/QTc intervals of the sinus complexes are normal (480/400 milliseconds).
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- © 2015 American Heart Association, Inc.